1. Field of the Invention
The present invention relates generally to an arrangement for controlling the transmission of light, and more particularly to a liquid crystal having electrode films thereon combined with a polarizer arrangement and a reflector.
2. Description of the Prior Art
Arrangements for controlling the transmission of light with the help of an electrode-coated liquid crystal cell in plate form placed between two polarizers and a reflector are known from DT-OS 2,158,563. In such devices it is preferable to use nematic liquid crystals, the molecules of which are disposed parallel to the electrode surfaces in a certain preferred direction. Between the two electrodes the molecules are so oriented that there is a continuous transition from the preferred direction in the boundry layer of one electrode to the preferred direction in that of the other, the molecules thus being arranged in helical fashion. In such known arrangements for controlling the transmission of light there was a 90.degree. twist of the liquid crystal between the electrode surfaces. Furthermore, two polarizers were always required.
Such an arrangement has the disadvantage that the output brightness often is not sufficient, because the incident light must pass through polarizing layers four times, resulting in a considerable loss of intensity since polarizing layers are not optically ideal and they absorb a significant portion of the light passing through even when aligned with the polarization direction of the incident light. Furthermore uniformity in liquid crystal readouts is frequently unattainable. This is probably connected with the formation of domain structures in liquid crystals. For instance with a 90.degree. twist in the crystal there can occur both right and left-hand twisted structures, which can therefore give rise to the formation of right- or left-hand twisted domains. At the boundary layers of such domains there are optical discontinuities which mar the appearance of the readout surface considerably by forming rings or stripes.